The primitive streak of an embryo.
What Does “Winter Solstice” Mean?The winter solstice lasts for just one moment. It occurs exactly when the Earth’s axial tilt is farthest away from the sun. This usually happens around December 21 or 22 in the Northern Hemisphere or June 20 or 21 in the Southern Hemisphere. If you’re in the Northern Hemisphere, during the solstice the sun will be at its southernmost point in the sky. The higher …
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.